The present invention relates generally to systems and methods for directing and controlling the operation of an induction motor and, more specifically, to systems and methods for enhancing the torque output of a field oriented induction motor operating in an overmodulation/field-weakening state.
he xe2x80x9cfuelxe2x80x9d powering a field oriented induction motor is current. This current may be divided into two components, torque current and flux current. Torque current may be viewed as that component of the current which generates motive force, or torque. Flux current may be viewed as that component of the current which generates magnetic flux in the rotor. Shaft torque and rotor flux are related, with shaft torque being proportional to the product of rotor flux times torque current.
Typically, the torque current and slip frequency of a field oriented induction motor, operating in a normal modulation state, are calculated using simple control parameters or equations which include two parts. The first part of these equations, commonly referred to as the feed forward or open loop portion, takes into account variables such as the reference or commanded torque, the flux feedback, the torque current, and the flux current. The second part of these equations, commonly referred to as the feedback or closed loop portion, takes into account variables such as the torque feedback and direct-axis back-EMF voltage feedback, as communicated to a proportional and integral controller (PI controller).
[t high speed, it is desirable for a field oriented induction motor to operate in an overmodulation/field-weakening state, maximizing the available torque. However, in such a state, feedback oscillates, current waveforms become non-sinusoidal, and the system becomes generally unstable. Thus, in an overmodulation/field-weakening state the equations discussed above break down, resulting in inaccurate torque current and slip frequency calculations, and diminished torque output.
The present invention overcomes the above problems and provides systems and methods for enhancing the torque output of a field oriented induction motor operating in an overmodulation/field-weakening state. Specifically, the present invention provides systems and methods for enhancing the conversion from a reference torque command to a processed torque current or slip frequency command.
In one embodiment, a system for enhancing the torque output of a field oriented induction motor includes a controller having a plurality of predetermined control parameters operable for processing input signals to generate output signals, the plurality of predetermined control parameters dependent upon the nature of the input signals and the operational state of the motor, and a sensor system operable for communicating feedback signals related to the output signals and the operational state of the motor from the motor to the controller.
In another embodiment, a method for enhancing the torque output of a field oriented induction motor includes, using a plurality of predetermined control parameters, processing input signals to generate output signals, the plurality of predetermined control parameters dependent upon the nature of the input signals and the operational state of the motor, and communicating feedback signals related to the output signals and the operational state of the motor from the motor to a controller.